1. Field of the Invention
The present invention relates to an image-shake correction apparatus for correcting a shake of an image and an imaging apparatus with the image-shake correction apparatus.
2. Description of the Related Art
Until now, an angular velocity sensor (hereinafter, sometimes referred to as gyroscope sensor) has been used for an imaging apparatus with an image-shake correction function to detect an amount of a shake. The gyroscope sensor vibrates a vibration member such as a piezoelectric element at a constant frequency and converts generated force due to the Coriolis force to voltage to obtain angular velocity information.
The obtained angular velocity is integrated to detect the amount of a shake. A shift lens capable of optically moving in an angle of view, for example, is moved in the direction in which the amount of a shake is cancelled to correct the shake of an image.
Japanese Patent Application Laid-Open No. 2006-319852, for example, discusses an image-shake correction technique for an imaging apparatus. The image-shake correction apparatus discussed in the application optimizes the frequency characteristic of a characteristic change unit according to temperature detected by a temperature detection unit. Thus, the frequency characteristic of the image shake correction is optimized over a wide frequency band regardless of the ambient temperature of a camera maim body. As a result, sufficient correction of an image shake can be achieved by a correction unit.
When the frequency characteristic of the characteristic change unit is optimized according to the temperature detected by the temperature detection unit, an optimal process can be applied to the image-shake correction apparatus according to a plurality of shooting modes.
Japanese Patent Application Laid-Open No. 2006-319852 discussed a method for optimizing the frequency characteristic of the characteristic change unit according to the temperature detected by the temperature detection unit. A gain is decreased as temperature rises to extend the temperature characteristic of a gyroscope sensor to a high frequency band. For this reason, the cutoff frequency of a high pass filter (hereinafter, referred to as HPF) is lowered at a low temperature and the cutoff frequency thereof is increased at a high temperature. Thus, the temperature characteristic is optimized in response to change in temperature.
Because of the recent miniaturization of a circuit board, a gyroscope sensor needs to be arranged adjacent to an integrated circuit (IC), which is a heat source. Increase in function of an IC increases heat emitted therefrom. Accordingly, the gyroscope sensor has been exposed to an increase in temperature.
As a result, a temperature drift phenomenon of an output of the gyroscope sensor has become influential. A sudden increase in temperature of the gyroscope sensor due to heat generated by the IC at the time of staring the camera main body significantly changes the output signal of the gyroscope sensor. As a result, even if the camera main body is not shaken, the camera erroneously determines that a shake occurs. That causes a significant problem in which an image stabilization performance is significantly degraded.
The above conventional technique merely optimizes the cutoff frequency of a HPF according to temperature of the gyroscope sensor or its vivinity to prevent the image stabilization performance from being degraded. For this reason, a direct current (DC) component cannot be sufficiently removed when the output of the gyroscope sensor is changed due to a sudden change in temperature.
More specifically, when temperature is not so high even after the sudden change of the temperature, for example, such a case in which temperature is increased from a low temperature, the cutoff frequency of the HPF is not set high, thereby the image-shake correction apparatus will be affected by the output change due to the temperature drift.
On the other hand, if temperature is suddenly lowered from a high temperature, change in output is caused due to temperature drift similarly with the case where temperature is increased. In this case, the cutoff frequency of the HPF is reduced in the above conventional technique to cause the camera to be affected by change in output due to temperature drift.
The increase of the cutoff frequency of the HPF at a high temperature results in increase in phase lead at a low frequency band. That causes the cutoff frequency HPF condition to be not best for a shake of a low frequency band. As a result, a shake of an image in shooting a still image at a slow shutter speed cannot be corrected.